It seems that in significant digits mode the trailing zeros setting is switched on by default and can't be switched off. Two proposals
1. (feature request) please allow for deactivating trailing zeros in both precision modes
2. (bug report) the trailing zero mode should display as on even if it can't be changed (check mark is missing in the context menu),
I'd recommend to have sort of toolbar which is displayed as soon as the cursor is on a result.
The toolbar could indicate the current settings of that result and allow to change them using the mouse or shortcuts
Of course this should affect only digits to the right of the decimal point.